1. Field of the Invention
The present invention generally relates to a photoelectric encoder, and more particularly, relates to a photoelectric encoder employing a shifting encoder scale, which is used for measurement of position and for detecting movement amount of a moving object in various machine tools, semiconductor manufacturing devices, and the like.
2. Description of the Related Art
In a conventional photoelectric encoder, light-detecting elements are arranged to have different four phases, i.e., A phase, B phase, /A phase and /B phase with a phase difference of P/4 with respect to an input signal pitch P, and each of the light-detecting elements has a width of P/2. The light-detecting elements are arranged in parallel with respect to a movement direction of a shifting scale, and four light-detecting elements having respectively different phases are combined into one set and a plurality of sets of the light-detecting elements are arranged in the movement direction of the shifting scale, so that a shift amount of the shifting scale is detected. Thus, a movement amount or a relative position of a moving object is detected, as corresponding to the shift amount of the scale. In this arrangement, a light source is positioned on a side opposite to the scale side, and duty ratio of the scale is set to 50%. See, for example, Paragraph 0008, FIG. 2 of Patent Document 1: Japanese Patent Laid-open Publication No. 8-201117.
In another conventional example of a photoelectric encoder, light-detecting elements are specified for A phase, B phase, /A phase and /B phase, each having a phase difference of P/4 with respect to an input signal pitch P, and the light-detecting elements are arranged with an interval of 3P/4 with respect to a scale shifting direction, so that a shift amount (i.e., movement amount) of the scale is detected. See, for example, Paragraphs 0067 to 0069, FIG. 10 of Patent Document 2: Japanese Patent Laid-open Publication No. 2002-236033.
It is noted here that the term “pitch P” is an interval of respective light-transmitting slits that are formed in the scale, and the pitch P corresponds to a cycle of an input signal obtained through the scale. Moreover, in the description of the present specification, with respect to the terms “A phase”, “B phase”, “/A phase” and “/B phase”, it is noted that “/A phase” and “/B phase” represents complementary relationships of inversion differential signals (with a phase difference of 180 degrees) with respect to “A phase” and “B phase”, respectively.
However, in the above-mentioned conventional photoelectric encoder, since the pitch is too narrow, it is not possible to provide a space for forming a cross-talk preventive portion, resulting in disadvantages such that a light signal deflects and reach the light-detecting elements and that a cross-talk may be undesirably generated between adjacent light-detecting elements. For preventing such s cross-talk, there may be considered a method in which the width of each light-detecting element is made smaller than P/2. However, if the width of the light-detecting element is reduced, the signal output thereof is undesirably reduced.
Moreover, the conventional photoelectric encoder has a complex wiring structure with wires mutually overlapping at some places, and therefore manufacturing of a light-detecting element array is made difficult.